Torch Down Roofing
Modified Bitumen. Proven Flat Roof Protection

Torch-Down Is an Old-School Trade — and Not Everyone Should Be Doing It

There's a reason I put this warning at the top of the page: torch work is dangerous. You're running a propane torch at around 2,500 degrees Fahrenheit across a roof deck, melting asphalt-based membrane onto whatever's underneath. Every year somewhere in California, somebody starts a house fire torching a roof because they got sloppy with the fire watch, left a smoldering rag under the eaves, or didn't catch an ember that dropped into a cavity. We don't take on torch-down jobs lightly, and we don't let every crew run a torch. It's a specialty.

That said — when it's done right, torch-applied modified bitumen is one of the best flat-roof systems you can put on an East Bay home. Thick, puncture-resistant, easy to repair, and familiar enough that any competent roofer in 20 years will know how to fix it. For residential garage roofs, small commercial, room additions, and covered patios, it's our go-to for a lot of situations.

What Is Torch-Down Roofing

Torch-down is the common name for modified bitumen roofing applied with an open flame. The membrane itself is asphalt that's been blended with polymer modifiers — either SBS (styrene-butadiene-styrene), which gives the asphalt rubber-like elasticity, or APP (atactic polypropylene), which gives it plastic-like heat resistance. It ships in rolls about 39 inches wide, reinforced with a polyester or fiberglass mat for tensile strength, and the underside has a thermoplastic film that melts when you hit it with a propane torch. That melted bitumen is the adhesive. Roll the membrane forward, torch the seam, and you've got a continuous waterproof skin that's bonded to the layer underneath.

The modified bitumen standards are ASTM D6162 (SBS polyester reinforced), D6163 (SBS fiberglass reinforced), and D6164 (SBS/APP hybrid). Every product we install meets one of those, plus CRC R905.14 for code compliance.

When Torch-Down Makes Sense

• Residential flat additions and garage roofs under about 1,500 sq ft where the job is too small to mobilize a TPO welder efficiently.
• Covered patios and sunrooms attached to pitched-roof houses — easy tie-ins, good puncture resistance, and the granulated cap sheet looks better than white membrane on a visible surface.
• Older commercial buildings where the original system was built-up or modified bitumen, and we're re-roofing in kind.
• Roofs where the owner wants a system they can patch themselves in 10 years with a bucket of roof cement and a torch. Modified bitumen is the most repair-friendly flat-roof system there is.
• Layered redundancy. A two-ply or three-ply modified bitumen system has built-in backup — if the cap sheet gets punctured, the base ply is still watertight. That redundancy is why it's lasted on commercial buildings for 50-plus years.

When torch-down doesn't make sense: anywhere you've got combustible materials close to the roof edge (wood siding within a few feet of the flame zone, overhanging branches, dry landscape below), large commercial areas over 3,000 sq ft (TPO or EPDM is faster and cheaper per square), and Title 24 cool-roof projects where the dark granulated surface won't hit the reflectivity threshold without a coating.

Brands and Product Lines We Install

• GAF Ruberoid — Ruberoid Mop Plus, Ruberoid Torch Granule, Ruberoid SBS Heat-Weld. The biggest name in modified bitumen and our most-specified product line. As a GAF Master Elite contractor, we can write Golden Pledge warranties on Ruberoid systems that most contractors can't touch.
• Firestone/Holcim AP Torchdown — APP-modified cap sheet with excellent heat and UV resistance. Good fit for sun-exposed East Bay inland roofs in Livermore, Antioch, and Brentwood.
• Soprema SOPRALENE — French-made SBS cap sheet, premium quality, thicker and heavier than the US standard products. What we reach for when the spec calls for the best of the best.
• Johns Manville DynaGlas and DynaWeld — fiberglass-reinforced SBS, broad product line covering base sheets through cap sheets.
• Henry Blueskin cap sheets and base sheets — Henry's self-adhered product line is what we use when torch application isn't safe for the conditions.

Installation — The Actual Sequence

Here's how a two-ply SBS torch-down job comes together on a typical East Bay residential flat addition:

1. Tear off the existing membrane to the deck. Replace any rot, soft spots, or swollen plywood.
2. Install cover board or recovery board — usually DensDeck Prime or a high-density wood fiber board. This gives the base sheet something solid to bond to and provides a thermal barrier between the torch and the wood deck below.
3. Mechanically fasten the base sheet or torch-apply it, depending on the deck type and the spec. Base sheet gives the cap sheet a bondable substrate and adds the first waterproof layer.
4. Fabricate flashings at pipe penetrations, parapet walls, scuppers, and HVAC curbs. This is detail work that separates a 10-year roof from a 25-year roof.
5. Torch the cap sheet. Unroll the cap, torch the underside as you go, and press the membrane down into the melted bitumen. Seam laps get 6 inches minimum overlap with a visible bead of molten bitumen at the lap edge — if you can't see the bleed-out, the seam isn't welded.
6. Fire watch. Every torch-down job gets an hour of fire watch after the last torch is shut down. Crew walks the perimeter, checks every penetration, probes the edges. California requires this by law for hot work, and we do it whether we're legally required or not.
7. Final walkthrough and permit signoff.

We carry fire extinguishers on every torch-down crew, pre-brief the homeowner about the fire-watch requirement, and check the CAL FIRE red flag warning status every morning before starting. On a red flag day, we reschedule. No exceptions.

Code Requirements

Modified bitumen is covered under CRC R905.14 and ASTM D6162/D6163/D6164 depending on reinforcement type. A properly assembled two-ply or three-ply modified bitumen roof over fire-rated insulation and cover board meets Class A fire rating under UL 790, which is required under Chapter 7A for any home in a Wildland Urban Interface zone. The assembly has to be installed as tested — swap out the cover board for something cheaper and you've voided the Class A rating.

Hot work permits are mandatory in most jurisdictions. Contra Costa County, Alameda County, and every city within them require a hot-work permit for torch application on roofs, and that permit carries fire-watch requirements, extinguisher requirements, and on-site fire safety documentation. We pull these permits as part of the job. If another contractor is quoting torch-down and not mentioning the hot work permit, that's a red flag.

Pricing and Timeline

Torch-down modified bitumen runs $500 to $1,000 per square installed. Single-ply cap over an existing sound base is at the low end. A full three-ply premium system with tapered insulation, fire-rated cover board, and custom parapet flashings is at the high end. A typical 1,000 sq ft residential flat section runs $6,500 to $11,000. A 3,000 sq ft small commercial job runs $18,000 to $28,000.

Timelines are quick: most residential jobs finish in 2 to 3 days. Commercial jobs run 3 to 5 days per 3,000 sq ft. Weather matters — we don't torch in the rain, on red flag days, or when the wind is strong enough to blow the torch flame off its target.

East Bay Cities Where Torch-Down Works Best

• Walnut Creek, Lafayette, and Orinda residential flat additions and garage roofs.
• Concord, Pleasant Hill, and Martinez older commercial buildings in kind with existing modified bitumen.
• West Oakland, Berkeley, and Albany Victorian and craftsman homes with flat additions on the back.
• Smaller downtown commercial blocks in Antioch, Pittsburg, Richmond, and San Leandro where the building stock is aging and the owners want a familiar system.
• Anywhere the original roof was torch-down or BUR and the owner wants continuity with what's been working.

Frequently Asked Questions

Call Us About Your Torch-Down Project

If you've got a flat roof, garage, addition, or covered patio that needs a modified bitumen system — or a leaking torch-down roof that needs someone who actually knows how to repair it — call East Bay Roofers at (925) 722-4916. We're CA #987654 C-39, GAF Master Elite, and we've been torching flat roofs across the East Bay since 1988. We pull the permits, we run the fire watch, and we don't cut corners on the safety side.